1. Field of the Invention
The invention relates to a video signal processing apparatus comprising means for generating video signals to enable the display of still or motion pictures on a connected display device, and means for generating a test signal to enable the display of a test image to facilitate user adjustment of a property of the display device to a correct setting which provides optimum representation of the pictures.
Such apparatuses include television receivers, where the display device is included in the apparatus, but also VCR's and other video and interactive video reproduction apparatuses, including CDV, CD-I, Laservision, Photo-CD and computer workstations, where the display device usually comprises a separate monitor or TV receiver.
The invention further relates to a method of storing pictures on a record carrier for subsequent reproduction via a display device having at least one user-adjustable display property, the method comprising:
(a) storing picture information on the record carrier in a form suitable for reproduction by the display device;
(b) defining a test signal suitable for causing the display of a test image including a first image feature imperceptible at a display property setting which is correct for the display of the stored pictures but visible when the display property deviates in a given direction from the correct setting; and
(c) storing information defining the test signal on the record carrier together with the picture information, characterized in that the first image feature, when visible, forms at least part of a symbolic instruction to the user indicating the nature of the deviation and/or the necessary corrective adjustment.
The accurate representation of pictures by the display device used with such apparatuses requires proper setting of the black level (brightness) and other properties of the display device (color, contrast etc.). This is particularly important when display devices such as cathode ray tubes (CRTs) and liquid crystal displays (LCDs) are used to represent natural photographic images, since CRTs and LCDs have very low dynamic range (contrast ratio) compared with photographic film. This makes it important to utilize fully the dynamic range that is available, by correct brightness setting.
2. DESCRIPTION OF THE RELATED ART
It is known that test images are useful tools in the setting of black levels, and DE-A-2 716 212 (PHD 77024) proposes a television receiver with a built-in test pattern generator. This test pattern, in common with many broadcast `testcard` patterns, includes adjoining regions of black and dark grey. If the brightness is set too low, the black and grey are indistinguishable, whereas, if the setting is correct, they are just visible as distinct features. The adjustment is necessary to maintain optimum dynamic range as viewing conditions (especially ambient lighting) change.
A first problem with the known test images is that the person making the adjustment requires to know the significance of the pattern, and the correct procedure for its utilization. In practice, only an engineer, if anybody, uses the known test patterns. This may be satisfactory, for example, in a professional studio environment, where engineers are available and where the ambient lighting conditions are constant and carefully controlled. However, the problem addressed here and in DE-A-2 716 212 is that, in the domestic and general business environment, engineers are not available, while the viewing conditions can vary widely and frequently.
Another problem with the test pattern proposed in DE-A-2 716 212, and with the known broadcast test patterns, is that the unskilled user, even with reference to an instruction manual, is required to judge when the difference between the black and grey regions is "just perceptible". There is no visual confirmation to prevent the user adjusting the black level too low, since the two shades displayed remain discernible at all brightness settings above the correct one.
In the professional studio engineering environment, test signal generators are known in which an area below black level is included adjoining a black area in addition to an above-black (grey) area. See for example Quinn and Siocos: "Pluge Method of Adjusting Picture Monitors in Television Studios--A Technical Note", Journal of the SMPTE Vol. 76 p 925 (September 1967). In such a case, the setting is correct when the above-black level is discernible, but the black and below-black areas are indistinguishable. Such test patterns are also commonly recorded before program material on video tapes in professional environments. Such a test pattern is not known to have been broadcast or included in a domestic television set or video recording, however, and in any event its significance and the manner of its exploitation are not readily appreciated by the average professional or domestic user.